It is known, that with a view to taking off, the leading edge slats, the flaps and the ailerons of an aircraft are imparted with a configuration optimizing the fineness (lift/drag ratio) of the latter, such that climbing slope becomes maximum. Now, in such a fineness optimization configuration, said ailerons occupy a position being partially deflected downwards. As a result, when the aircraft has an optimized fineness as soon as it has left the ground, the drag of said aircraft cannot be optimal as long as the latter runs while accelerating on the ground.